High-precision control of the rotational motion of an AC rotating machine requires information relating to the rotational position of the AC rotating machine, and information relating to the current flowing in the windings of the AC rotating machine. The rotational position of an AC rotating machine may in some instances be acquired by a rotational position sensor that is provided separately in the AC rotating machine.
However, separately providing a rotational position sensor in the AC rotating machine is significantly disadvantageous in terms of cost reduction, space saving and increasing reliability. Therefore, a rotational position estimation function is required in order to realize sensorless rotational position sensing.
Moreover, a configuration in which the AC rotating machine is controlled using an estimated rotational position allows for continued operation of the AC rotating machine even in cases of malfunction of the rotational position sensor. Therefore, a rotational position estimation function is also required in order to cope with malfunction of a rotational position sensor.
Therefore, the dependence of induced voltage on rotational position in a synchronous motor has been exploited conventionally to estimate rotational position on the basis of the voltage applied to the synchronous motor, the current flowing in the synchronous motor, and the electrical constants of the synchronous motor (see for instance PTL 1, NPL 1 and NPL 2). The rotational position estimation scheme disclosed in PTL 1, NPL 1 and NPL 2, referred to as “induced voltage scheme” is a widely recognized scheme.